US9443551B1 - Method and system for writing and reading closely-spaced data tracks - Google Patents
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- US9443551B1 US9443551B1 US14/687,620 US201514687620A US9443551B1 US 9443551 B1 US9443551 B1 US 9443551B1 US 201514687620 A US201514687620 A US 201514687620A US 9443551 B1 US9443551 B1 US 9443551B1
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- 238000000034 method Methods 0.000 title claims abstract description 27
- 238000001514 detection method Methods 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 230000002452 interceptive effect Effects 0.000 description 2
- 238000013500 data storage Methods 0.000 description 1
- 238000004193 electrokinetic chromatography Methods 0.000 description 1
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
- G11B20/10—Digital recording or reproducing
- G11B20/12—Formatting, e.g. arrangement of data block or words on the record carriers
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/02—Recording, reproducing, or erasing methods; Read, write or erase circuits therefor
- G11B5/09—Digital recording
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
- G11B20/10—Digital recording or reproducing
- G11B20/10009—Improvement or modification of read or write signals
- G11B20/10305—Improvement or modification of read or write signals signal quality assessment
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
- G11B20/10—Digital recording or reproducing
- G11B20/12—Formatting, e.g. arrangement of data block or words on the record carriers
- G11B20/1217—Formatting, e.g. arrangement of data block or words on the record carriers on discs
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
- G11B20/10—Digital recording or reproducing
- G11B20/18—Error detection or correction; Testing, e.g. of drop-outs
- G11B20/1833—Error detection or correction; Testing, e.g. of drop-outs by adding special lists or symbols to the coded information
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/012—Recording on, or reproducing or erasing from, magnetic disks
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/02—Recording, reproducing, or erasing methods; Read, write or erase circuits therefor
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
- G11B20/10—Digital recording or reproducing
- G11B20/10009—Improvement or modification of read or write signals
- G11B20/10305—Improvement or modification of read or write signals signal quality assessment
- G11B20/10361—Improvement or modification of read or write signals signal quality assessment digital demodulation process
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
- G11B20/10—Digital recording or reproducing
- G11B20/12—Formatting, e.g. arrangement of data block or words on the record carriers
- G11B20/1217—Formatting, e.g. arrangement of data block or words on the record carriers on discs
- G11B2020/1218—Formatting, e.g. arrangement of data block or words on the record carriers on discs wherein the formatting concerns a specific area of the disc
- G11B2020/1238—Formatting, e.g. arrangement of data block or words on the record carriers on discs wherein the formatting concerns a specific area of the disc track, i.e. the entire a spirally or concentrically arranged path on which the recording marks are located
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
- G11B20/10—Digital recording or reproducing
- G11B20/12—Formatting, e.g. arrangement of data block or words on the record carriers
- G11B2020/1291—Formatting, e.g. arrangement of data block or words on the record carriers wherein the formatting serves a specific purpose
- G11B2020/1292—Enhancement of the total storage capacity
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
- G11B7/14—Heads, e.g. forming of the optical beam spot or modulation of the optical beam specially adapted to record on, or to reproduce from, more than one track simultaneously
Definitions
- This disclosure relates to data storage systems of the type in which read and write heads move over tracks of data on a storage medium. More particularly, this disclosure relates to the writing and reading of data tracks that are closely-spaced with an adjacent track or tracks.
- data may be written in circular (or sometime spiral) tracks on a magnetic disk.
- minimum track pitch is limited by the write head width, while the read head is designed to be narrower than the write head so that reading can occur without picking up signals from any adjacent track.
- guard bands empty bands on either side of each track—are provided to help prevent data on one track from being overwritten during writing of an adjacent track because of write head positioning errors.
- a method for writing data onto a medium on which data are stored in tracks includes encoding the data into at least one codeword, and writing a respective portion of each of the at least one codeword onto respective different tracks on the medium.
- the writing may include writing a respective portion of each of the at least one codeword onto respective different adjacent tracks on the medium.
- the method may further include dividing the codeword symmetrically to form each respective portion.
- the dividing may include apportioning all of any one symbol in the codeword to a single one of the different adjacent tracks.
- the dividing may include apportioning portions of any one symbol in the codeword to different ones of the different adjacent tracks.
- the dividing may instead include dividing the codeword asymmetrically to form each respective portion.
- Another method for reading data that have been encoded into codewords includes positioning a plurality of read heads to read codewords that have been written across multiple tracks of a medium, with the plurality of read heads being positioned relative to a first group of the multiple tracks so that each read head in the plurality of read heads reads a different portion of the first group of the multiple tracks, and where each different portion of the multiple tracks overlaps at least one other different portion of the multiple tracks. Signals are detected from the plurality of read heads, and the detected signals are decoded.
- a storage device may include a storage medium having thereon more than one track of data that have been encoded into codewords, and reading apparatus.
- the reading apparatus includes a plurality of read heads for positioning to read codewords that have been written across multiple tracks of a medium, with the plurality of read heads being for positioning relative to a first group of the multiple tracks so that each read head in the plurality of read heads reads a different portion of the first group of the multiple tracks, and where each different portion of the multiple tracks overlaps at least one other different portion of the multiple tracks.
- Detector circuitry detects signals from the plurality of read heads, interleaver circuitry combines the detected signals, and decoder circuitry that decode the combined detected signals.
- Another storage device includes writing apparatus that writes to a storage medium having more than one track of data that have been encoded into codewords, with each codeword being written across multiple tracks of the medium.
- the writing apparatus includes encoder circuitry that encodes the data into at least one codeword, and controller circuitry that causes the write head to write each respective portion of each of the at least one encoded codeword onto respective different tracks on the medium.
- FIG. 1 shows a simplified schematic view of a portion of a storage device
- FIG. 2 shows a first writing scenario
- FIG. 3 shows a second writing scenario
- FIG. 4 shows a reading scenario
- FIG. 5 shows a simplified read channel
- FIG. 6 shows a known arrangement of codewords along tracks of a storage medium
- FIG. 7 shows an arrangement of codewords along tracks of a storage medium in accordance with this disclosure
- FIG. 8 shows a simplified write channel
- FIG. 9 shows an exemplary codeword
- FIGS. 10 and 11 show examples of apportionment, among multiple tracks, of two-bit symbols in a codeword
- FIGS. 12 and 13 show examples of apportionment, among multiple tracks, of three-bit symbols in a codeword
- FIG. 14 shows a portion of a read channel according to implementations of this disclosure
- FIGS. 15 and 16 show portions of a read channel according to implementations of this disclosure using iterative decoding
- FIG. 17 is a flow diagram of an exemplary method according to this disclosure.
- FIG. 18 is a flow diagram of another exemplary method according to this disclosure incorporating a re-try mode.
- This disclosure relates to a method and system for writing data to, and reading data from a data track that may overlap with one or more adjacent data tracks.
- codewords may be written (or “interleaved”) across multiple tracks.
- the disclosure applies to any number of read heads (as long as there are at least two read heads) and any number of tracks up to the number of read heads (as long as there are at least two tracks).
- there may be m read heads and codewords may be interleaved across n tracks, where m ⁇ 22, n ⁇ 22, and n ⁇ m.
- FIG. 1 shows a simplified schematic view of a portion of a storage device showing four adjacent data tracks 101 , 102 , 103 , 104 on a storage medium 100 , with two read heads 105 , 106 .
- Read heads 105 and 106 are positioned so that both read heads 105 and 106 are over tracks N ( 102 ) and N+1 ( 103 ), with read head 105 mainly over track N ( 102 ) and read head 106 mainly over track N+1 ( 103 ).
- the tracks are shown in this and other drawings as being straight, in reality, on the surface of a disk drive platter, the tracks ordinarily would be curved.
- data may be written “downtrack”—i.e., along each track 102 , 103 , and by reading portions of the two tracks 102 , 103 twice using the two read heads 105 , 106 , inter-track interference may be cancelled out to provide clean data from each of tracks 102 , 103 .
- FIGS. 2 and 3 The writing operation for the known scenario is shown for three tracks N ( 102 ), N+1 ( 103 ) and N+2 ( 104 ) in FIGS. 2 and 3 .
- each of write heads 202 , 203 , 204 writes to one of tracks N ( 102 ), N+1 ( 103 ) and N+2 ( 104 ), respectively.
- write heads 202 , 203 , 204 maintain alignment with tracks N ( 102 ), N+1 ( 103 ) and N+2 ( 104 ), respectively, resulting in tracks of uniform pitch.
- a real scenario is more likely to resemble FIG.
- ITI inter-track interference
- two read heads so arranged can be used to derive data from both of the two adjacent tracks.
- the read heads would first be placed over tracks N ( 102 ) and N+1 ( 103 ) to read track N ( 102 ), then over tracks N+1 ( 103 ) and N+2 ( 104 ) to read track N+1 ( 103 ), then over tracks N+2 ( 104 ) and N+3 ( 107 ) to read track N+2 ( 104 ), and then over tracks N+3 ( 107 ) and N+4 (not shown) to read track N+3 ( 107 ).
- read heads 105 , 106 would first be placed over tracks N ( 102 ) and N+1 ( 103 ) to read tracks N ( 102 ) and N+1 ( 103 ), then over tracks N+2 ( 104 ) and N+3 ( 107 ) to read tracks N+2 ( 104 ) and N+3 ( 107 ).
- n 2
- read throughput would be doubled; more generally, read throughput would be increased by a factor of n.
- interleaved detection and decoding as described below may have improved results in instances where the signal-to-noise ratio (SNR) is not uniform across the different tracks, making decoding failure less likely. Similarly, there may be an improved bit-error ratio across tracks.
- SNR signal-to-noise ratio
- FIG. 5 shows a simplified read channel 500 including read heads 105 , 106 denoted as H 1 and H 2 , reading from two adjacent tracks N ( 102 ) and N+1 ( 103 ).
- the signals output by heads 105 , 106 may be denoted as R H1 and R H2 .
- the data sequences represented by signals R H1 and R H2 are processed first by front end 501 , which includes an analog-to-digital converter and front-end demodulation to provide digital signals Y H1 and Y H2 . Detection and decoding of signals Y H1 and Y H2 in accordance with embodiments of this disclosure occur in back end 502 , as discussed below.
- a disk drive controller 503 coordinates the operations of front end 501 and back end 502 , as well as the operations of the write channel (not shown in this drawing), the spindle motor that rotates the storage medium 100 , and the stepper motor that controls movement of the read heads 105 , 106 and the write heads 202 , 203 , 204 .
- codewords may be interleaved across tracks.
- each codeword is of size K bits
- all K bits of one codeword 601 would be written along track N ( 102 ) and all K bits of another codeword 602 would be written along track N+1 ( 103 ).
- the K bits of each codeword are divided across n tracks. This may be done symmetrically, with K/n bits written to each of the n tracks, or asymmetrically (i.e., a different fraction of the K bits is written to each track).
- K/2 bits of each codeword 701 , 702 are written to each of the two tracks, track N ( 102 ) and track N+1 ( 103 ).
- FIG. 8 shows a circuit arrangement 800 in a write channel for encoding data according to embodiments of this disclosure.
- Incoming data 801 is encoded in encoder 802 using a suitable error correcting code (ECC), which may be a low-density parity check (LDPC) code.
- ECC error correcting code
- LDPC low-density parity check
- One class of ECC codes that may be used in accordance with some implementations is a non-binary LDPC code.
- suitable ECCs such as Turbo Codes, Bose-Chaudhuri-Hocquenghem (BCH) codes, or Reed-Solomon codes, can be used.
- BCH Bose-Chaudhuri-Hocquenghem
- the apportionment of data onto the different tracks may be controlled by data divider 803 , which can be a general interleaver block. Symmetric division has been shown for simplicity but, as noted above, asymmetric arrangements also are possible. Thus, data divider block 803 may assign a different “codeword chunk” size to each track. If the division is symmetrical, the codeword chunk sizes are all the same.
- FIGS. 9-13 show examples of how data may be divided across tracks.
- FIG. 9 shows the first five two-bit GF( 4 ) LDPC symbols 901 - 905 of a codeword 900 to be allocated. As shown in FIG. 10 , each of symbols 901 - 905 is apportioned symmetrically (one bit per track) across two tracks N ( 102 ) and N+1 ( 103 ). Alternatively, in FIG. 11 , codeword 900 is symmetrically allocated across tracks N ( 102 ) and N+1 ( 103 ), but each individual symbol 901 - 906 is written along a single one of tracks N ( 102 ) and N+1 ( 103 ).
- FIGS. 12 and 13 show how a codeword including three-bit GF( 8 ) LDPC symbols may be apportioned.
- the codeword is symmetrically allocated across tracks N ( 101 ) and N+1 ( 102 ), with each of symbols 1201 - 1204 written along a single one of tracks N ( 101 ) and N+1 ( 102 ).
- the codeword is symmetrically allocated across tracks N ( 101 ) and N+1 ( 102 ), with each of symbols 1301 - 1304 allocated asymmetrically (because there are three bits) across tracks N ( 101 ) and N+1 ( 102 ).
- Whether the allocation of symbols is along the track, or across tracks, may depend on the amount of underlying ITI across the tracks, and the amount of inter-symbol interference (ISI) along each track, respectively.
- ISI inter-symbol interference
- the data over which the read heads pass is first detected and then decoded.
- the detector is m-dimensional—i.e., the detector operates on m inputs and produces n outputs—while the decoder operates on the inputs from the n tracks and provides n corresponding outputs.
- the number of tracks over which the codeword is interleaved may be any number, but to support full throughput, the number of tracks over which the codeword is interleaved should be no greater than the number of detector inputs—i.e., n m—so that decoding may be performed in real time, or “on the fly,” particularly if multiline read heads are used.
- Multi-track detector 1401 may be any suitable detector capable of operating on multi-dimensional signals Y H1 -Y Hm , and providing output 1402 which may be soft output and/or hard output.
- detector 1401 may be an m-dimensional Viterbi detector, or an m-dimensional Bahl-Cocke-Jelinek-Raviv (BCJR) detector.
- detector 1401 operating on m input signals, may be capable of using the m inputs to deal with inter-track and inter-symbol interference.
- the detector outputs 1402 which may be hard decisions or soft information (such as, e.g., binary log-likelihood ratios) may be combined by data combiner 1403 , which may be the inverse of data divider 803 , combining the detector outputs symmetrically or asymmetrically according to a selected pattern into n tracks.
- the combined n-track outputs 1404 are then decoded by decoder 1405 .
- detector 1401 is most advantageously an m-input detector with n outputs
- an m-input detector with n′ outputs (assuming n ⁇ n′ ⁇ m) also may be used, even though the result may be less optimal.
- n out of n′ outputs of the detector are used as inputs to the decoder. This arrangement is possible only in the TDMR case of n ⁇ m.
- the decoder may be an iterative decoder 1505 .
- the outputs of detector 1501 are soft extrinsic detector outputs 1502
- the outputs of decoder 1505 are soft extrinsic decoder outputs 1506 .
- Data divider 1507 is again like data divider 803 , providing soft information such as soft a priori detector information 1508 to detector 1501 .
- the information from the ECC decoder 1505 to multi-track detector 1501 is provided in all n tracks (across-track) as well as in the usual along-track or downtrack fashion. Providing extrinsic information across tracks may contribute to improved ITI cancellation task in detector 1501 , whether the information provided by decoder 1505 is soft or hard.
- interleaved detection and decoding as described herein may have improved results in instances where the signal-to-noise ratio (SNR) is not uniform across the different tracks.
- SNR differences may result because, as shown in FIG. 3 , write head positioning may vary, resulting in different track widths. Wider tracks generally have better SNR than narrower tracks.
- a codeword written to narrower track would exhibit a worse SNR than a codeword written to a wider track, and hence the decoder is more likely to fail on the codeword written to the narrower track.
- SNR signal-to-noise ratio
- each codeword in which each codeword is spread across multiple tracks, even if one part of a codeword is written to a narrower track, it is likely that the adjacent track, to which the other part of that codeword is written, would be wider. Therefore, the codeword would not suffer the worst-case SNR and a decoding failure would be less likely. Similarly, there may be an improved bit-error ratio across tracks.
- data divider 803 / 1507 and data combiner 1403 / 1503 , is to align bit positions correctly where the error-correcting code is a binary code that provides log-likelihood ratios in a binary domain.
- This function may be provided by a data interleaver 1603 and de-interleaver 1607 as shown in partial read channel 1600 of FIG. 16 .
- interleaver 1603 and de-interleaver 1607 may operate to align information on a symbol level rather than a bit level, again in either across-track or downtrack modes.
- Method 1800 begins at 1801 where m read heads are positioned (e.g, in the manner described above) relative to n tracks for reading the n tracks. At 1802 signals from the m read heads are used to detect n tracks, and at 1803 , the detected signals are decoded.
- An optional “re-try mode,” which can re-try the decoding either once or N times may be selected at 1804 .
- N may be the same as n, where n is the number of tracks as discussed above. If re-try mode is not selected (because a single pass is considered sufficient), the method ends. If “re-try once” is selected, then some or all of the m read heads are again positioned, at 1805 , relative to the n tracks to favor a track that may have produced a weaker signal on the previous pass. The re-positioned read heads are used to obtain new data to input to the detector. The newly-obtained data for the newly-favored track at the input of the detector (e.g., data Y H1 shown in FIGS.
- 5 and 14-16 may replace the previous version of the data (e.g., replacing whatever data Y H1 was obtained at 1801 ), while some data may be kept (e.g., data Y H2 obtained at 1801 may be kept).
- signals are again detected from the newly-chosen data Y H1 , . . . , Y Hm .
- the detected signals are again decoded.
- the better result is selected.
- a counter is set to 1.
- some or all of the m read heads are again positioned relative to the n tracks to favor a track that may have produced a weaker signal on a previous pass.
- the re-positioned read heads are used to obtain new data to input to the detector.
- the newly-obtained data for the newly-favored track at the input of the detector e.g., data Y H1 shown in FIGS. 5 and 14-16
- may replace the previous version of the data e.g., replacing whatever data Y H1 was obtained at 1801
- some data may be kept (e.g., data Y H2 obtained at 1801 may be kept).
- the counter value j is incremented at 1820 , and the collection of data inputs for the detector continues.
- some or all of the m read heads are again re-positioned to favor one of the tracks.
- the newly re-positioned read heads are again used to obtain new data to input to the detector.
- the newly-obtained data for the newly-favored track at the input of the detector e.g., if the counter value j is 2, data Y H2 shown in FIGS. 5 and 14-16
- the m read heads are yet again re-positioned to favor a particular track.
- the newly re-positioned read heads are again used to obtain new data to input to the detector.
- the newly-obtained data for the newly-favored track at the input of the detector e.g., while not explicitly shown in FIGS. 5 and 14-16 , data Y Hj from among data Y H1 -Y Hm ) may replace the previous version of the data (e.g., replacing whatever data Y Hj was obtained at 1801 ).
- the counter value j will reach N, at which point, as discussed above, at 1818 , signals are again detected from the newly-chosen data Y H1 , . . . , Y Hm , and at 1819 , the detected signals are again decoded.
- the better result (from decoding 1803 and decoding 1818 ) is selected.
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US15/646,209 US10224063B1 (en) | 2014-04-16 | 2017-07-11 | Method and system for writing and reading closely-spaced data tracks |
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US9734848B1 (en) * | 2014-04-16 | 2017-08-15 | Marvell International Ltd. | Method and system for writing and reading closely-spaced data tracks |
US11404085B1 (en) | 2021-03-09 | 2022-08-02 | Kabushiki Kaisha Toshiba | Magnetic disk device and error correction processing method |
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JP2020042888A (en) * | 2018-09-13 | 2020-03-19 | 株式会社東芝 | Magnetic disk device and controlling method for magnetic disk device |
US11966623B2 (en) | 2022-04-11 | 2024-04-23 | Seagate Technology Llc | Increased aerial density capability in storage drives using encoded data portions written to media surfaces with different aerial density capabilities |
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